The field of this invention is downhole isolation devices and more specifically those devices that permit flow to the surface and are removable by milling or drilling.
In certain downhole operations, it is desirable to isolate a portion of the wellbore. This can occur when perforation a zone in a cased borehole. Another occasion is when fracturing a formation through a set of perforations in one zone and having to isolate the remainder of the wellbore from the applied pressures of that procedure. Usually, these barriers are temporary and need to be removed from the wellbore when a perforating or fracturing operation is concluded. For these reasons, these devices have been made with non-metallic materials to enhance drillability.
In the past, these devices have had a passage through them to permit flow toward the surface. When isolation between zones was needed, a ball was dropped from the surface to land on a seat in the isolation device and pressure was built up on the seated ball. There were two main disadvantages to this design. Even if the ball was run with the isolation device instead of being dropped in later the mill-out was problematic because the ball could rotate on the seat during the milling. So even though the isolation device was predominantly of non-metallic materials, the milling process was still prolonged. The other issue with the prior designs was that the ball was not retained to the isolation device so that flow towards the surface could bring the ball out with it and get it stuck in the blowout preventers, creating a safety concern. An example of this type of design is the FAS DRILL Bridge Plug offered by Halliburton. Other prior designs for zone isolation involved flapper type valves held open with a stinger or sliding sleeve designs operated with a stinger.
The present invention seeks to address the issue and solve the problems associated with the known devices. It comprises a non-spherical valve member that will not rotate during mill-out. The valve member is also retained so that it will not be carried uphole to wind up in the blowout preventers. Non-metallics are used to promote drillability. A plurality of the isolators of the present invention can be used and milled out after all the zones have been completed. These and other benefits of the present invention will be apparent to those skilled in the art from a review of the description of the preferred embodiment described below.
A downhole zone isolation device is disclosed that features a non-spherical valve member that will not rotate while being drilled out. The valve member is retained in the isolation device so that flow uphole will not allow the valve member to exit the body of the isolation device. Bypass passages around the valve member are provided so that flow uphole can lift the valve member off its seat and flow can go around its periphery. Pressure from above seats the valve member. Non-metallic materials speed drill-out.